Foldable tricycle frames are known which are folded and unfolded by hand, at times not without a certain amount of difficulty.
Italian Patent IT-981 018, for example, describes a foldable two-wheel vehicle frame comprising at least a first subframe in the form of an articulated quadrilateral and connected by means of at least one lever to a saddle fitted to a second subframe also in the form of an articulated quadrilateral. By manually deforming the second subframe, e.g. by pushing down the saddle, the first subframe is deformed so that the rear wheel of the vehicle moves towards the front wheel, thus reducing the length of the vehicle.
Italian Patent IT-1 262 538 describes the front subframe of a vehicle with two or more wheels, in which the handlebar and the front wheel are connected by a mechanism, so that, once the handlebar is detached from a fastening hook, downward rotation of the handlebar about a hinge shifts a connecting rod, which in turn rotates the front fork about another hinge, thus simultaneously lowering the handlebar and moving the front wheel back to reduce the length and height of the vehicle.
Various documents describe mechanisms whereby each of the two lateral wheels of a tricycle can be moved manually towards the longitudinal plane of symmetry of the tricycle to reduce its width.
None of the above documents, however, considers the possibility of deforming the lateral subframes supporting the two lateral wheels of the tricycle, by deforming the central subframe of the tricycle.